Fans commonly are utilized in many applications such as, for example, for cooling electronic elements within a computer system. One such fan is shown in U.S. Pat. No. 4,656,553 (Brown), the disclosure of which is incorporated herein, in its entirety, by reference. The fan shown in Brown ("Brown fan") has been distributed under the trade name "THERMAPRO-V.TM.", distributed by Comair Rotron, Inc. of San Ysidro, Calif.
The Brown fan includes a rotor having a rotor magnet, and a stator having a pair of windings that magnetically interact with the rotor magnet. During operation, the windings are controlled by a winding supply circuit to rotate the rotor. Among other elements, the supply circuit includes a pair of power transistors that each power one of the two windings, a magnetic sensor for selectively energizing the power transistors, an adjustable voltage regulator for protecting the fan motor and controlling fan performance, and an external programmable element that cooperates with the regulator for externally controlling (i.e., programming) the speed of the fan.
The power transistors, programmable element, and regulator each are voltage drops in the winding circuit that reduce the effective voltage across the windings. Consequently, these three elements utilize a significant amount of the input voltage that is introduced to the circuit at the voltage input In addition to powering the three noted elements, however, the input voltage also energizes the windings. Accordingly, the input voltage must be sufficiently high to effectively energize the windings, in addition to the power transistors, programmable element, and regulator.
The regulator, which is disclosed as a conventional integrated circuit, may be internally adjusted by an adjust terminal to control the voltage at an output terminal of the regulator. This adjusting feature internally sets the speed of the fan so that one fan may be used for different applications. The voltage regulator also includes a thermal shutdown element and current regulator that together prevent the motor windings and the winding supply circuit from overheating due to receipt of too much current. Specifically, the current regulator limits the current to a maximum value and the thermal shutdown element shuts down the circuit for a predetermined time period if the voltage regulator reaches a preselected temperature. A number of discrete elements, such as Zener diodes and resistors, also are required to ensure that the voltage regulator operates as specified. Reference is made to Brown for a more detailed description of the voltage regulator and other features of the winding supply circuit.